Device and method of density measurement and control of flotation systems

ABSTRACT

Two open-end tubes are vertically immersed, open-end down at substantially the same level, one near the place of entrance of a liquid in process in a series of treating vessels and the other near the outlet of the liquid whereby densities of the liquid at the respective locations are measured by means of a suitable pneumatic assembly, the density values are translated to and recorded as a pneumatic pressure differential and the pneumatic pressure differential is either (1) automatically converted to and recorded in meaningful values and the indicated adjustments manually made to restore and tend to maintain the optimum density differential, or (2) directed to an optimizer whereby optimum adjustments are automatically made to restore and tend to maintain a maximum density differential. Where a fluctuating level of liquid exists, two probes immersed at different depths to define a fixed stratum may be used in cooperation to obtain one density value.

United States Patent 1 Hart [ Sept. 10, 1974 1 DEVICE AND METHOD OFDENSITY MEASUREMENT AND CONTROL OF FLOTATION SYSTEMS [75] Inventor:Porter Hart, Lake Jackson, Tex.

[73] Assignee: The Dow Chemical Company,

Midland, Mich.

22 Filed: Jan.20, 1972 211 App]. No.: 219,221

[52] us. c1 209/1, 209/166, 210/96 [56] References Cited UNITED STATESPATENTS 2,115,520 4/1938 Decker 73/438 2,125,663 8/1938 Wuensch209/l72.5 X

2,765,219 10/1956 Shawhan 235/1501 X 3,031,267 4/1962 Martin 235/1501 X3,094,484 6/1963 Rizo-Patron.. 209/164 X 3,207,305 9/1965 Custred209/166 X 3,333,695 8/1967 Van Note 210/96 X 3,427,198 2/1969 Hill73/439 X 3,460,394 8/1969 Cryer 73/439 3,462,364 8/1969 Carlson 210/42OTHER PUBLICATIONS Chem. Abst., 64, 1966, 15444c.

Quelvra c/io so /u for) Chem. Abst., 68, 1968, 89182K.

Chem. Abst., 69, 1968, 37996e.

Primary ExaminerRobert l-lalper Attorney, Agent, or Firm-A. CooperAncona [57] ABSTRACT Two open-end tubes are vertically immersed, openenddown at substantially the same level, one near the place of entrance ofa liquid in process in a series of treating vessels and the other nearthe outlet of the liquid whereby densities of the liquid at therespective locations are measured by means of a suitable pneumaticassembly, the density values are translated to and recorded as apneumatic pressure differential and the pneumatic pressure differentialis either (1) automatically converted to and recorded in meaningfulvalues and the indicated adjustments manually made to restore and tendto maintain the optimum density differential, or (2) directed to anoptimizer whereby optimum adjustments are automatically made to restoreand tend to maintain a maximum density differential. Where a fluctuatinglevel of liquid exists, two probes immersed at different depths todefine a fixed stratum may be used in cooperation to obtain one densityvalue.

8 Claims, 6 Drawing Figures 7 L1 (070/0 (llflc/ua al-l (0 0, 'v A (em/ e1 2 0 (EfTo/a/ 21 .9 mass 26 (3%,? 54 Prod 41c? -l-**'i l 7.9Jl L I J 1Ro/arg 81 Roz/96ers o T fiickener W0 fer recyc/e or lo wasfe PAIENTEBSEN 0:914

sum 1 via INVENTOR. fiorrer Horf QO Q 0% TTQRNEY DEVICE AND METHOD OFDENSITY MEASUREMENT AND CONTROL OF FLOTATION SYSTEMS BACKGROUND OFTHE'INVENTION In many processes conducted in liquid phase, it isessential for control thereof to ascertain and-control the density atvarious stages. Density differential very often is also indicative andsometimes an accurate measurement of the efficiency of the process.Illustrative of the latter are ore flotation systems wherein a mineralis separated by passing an aqueous slurry of finely ground orecontaining conditioning agents through a series of open-top chambers orvessels (usually called cells), psitioned substantially horizontally toeach other, each provided with an upwardly directed air supply andtroughs or trays along the upper edges thereof to collect and drain awaythe desired mineral which is frothed off, sometimes aided by additionalwater supplied to the collection system, and usually thereafterthickened and dried. For specific consideration the separation offluorite (which term will herein be used interchangeably withsubstantially pure CaF from fluorspar ore is illustrative. Fluoritewhich is the principal component of the ore and which is of greatestdensity, is frothed off as the slurry moves through the vessels,commonly called rougher cells. Accordingly, the density of the slurry islessened as it passes from cell to cell. The efficiency of the system isindicated by the difference in density of the slurry in the successivecells and particularly between the first and last cells of a series. Ingeneral, the greater the difference in density, the more of the desiredheavier mineral is being floated off.

Heretofore, density values have been obtained by manually taking samplesof the slurry as it enters the first cell and again as it leaves asubsequent cell, weighing the samples, and calculating the densitydifferential. Although this has long been done by a convenient litervessel attached to one end of a balance arm and having a calibratedspring scale attached to the other, such measurements are only roughlyaccurate, and also provide only periodic values; they do not provideadequate information for satisfactory control of the system. Not only issuch method of measurement done only at intervals so that conditionsbetween measurements are unknown, but the time lag between the time thatawareness of an undesirable change in density is known and a correctionis made and becomes effective leads to erratic results.

A need, therefore, exists for a method of continuous densitydifferential measurement and for prompt correction and particularly forautomatic correction to effectuate the greatest differential conduciveto frothing off a high quality product. The invention fulfills this needto a most gratifying extent.

SUMMARY OF THE INVENTION Broadly, the invention is a method ofcontinuously measuring density, and particularly the concurrentmeasurement of density values at two stages of progress in a liquidsystem to ascertain the density differential, and the apparatusnecessary for performing such method. The preferred mode of practicingthe invention consists of a method and apparatus which measures suchdensities and density differential and promptly and automaticallycorrects the density differential to provide optimum conditions.Particularly the invention is a method and apparatus which continuouslymeasures the differential between density values, converts such valuesinstantly to a pressure differential, optionally relates the densitydifferential to a calibrated recording instrument, to guide manualchanges if desired, and/or simultaneously makes proper changes in one ormore components of the source material being introduced into the system,whereby the density differential is optimized to maintain maximumrecovery of product of improved quality.

Although the term pH (which strictly means only the reciprocal of thelogarithm of the hydrogen ion concentration) is used herein to designateE.M.F. or electric potential produced in the slurry, it is to be bornein mind that such potential may be due in part to other contributingcauses.

DESCRIPTION OF THE INVENTION The invention is an improvement inflotation processes generally, and apparatus necessary for the practicethereof. To better understand the invention, conventional flotation,applicable to the recovery of CaF product from fluorspar, is set outbelow.

Ore is pulverized, as by passing it through a rockcrusher, grizzly, orthe like and then, after admixture with water to produce a slurry, someor all of the following treating agents are admixed therewith: a surfacetension improving agent (known sometimes as a collector) to increasesurface tension and to encourage bubble formation and stabilized froth,a suppressant to lessen the tendency of undesirable minerals present inthe ore to rise in the froth, and an alkalinity-control agent tomaintain desirable ionic potential in the slurry, and passing the sotreated slurry in sequence: through a ball mill to reduce particle size;from the ball mill to a conditioning tank (conditioner) for thoroughmixing and usually admixture of additional treating agents to attain adesired slurry composition for processing conditions; from theconditioner to a series of rougher cells wherein the slurry is agitatedand into which are fed upwardly directed air to produce a mass ofbubbles or froth, to which the desired mineral is attracted and adheresand which is caused to overflow out into collecting troughs positionedalong the outer edges of the cells; from the collecting troughs (usuallysome additional water being admixed with the froth at this point)optionally into a second series of similarly designed cells (oftencalled cleaners) by which the so collected foam is again subjected toair flotation and refined to a higher content of desired mineral; fromthe cleaners (or directly from the roughers) into a slowly agitatedmoderately heated tank (usually called a thickener) during whichentrapped air escapes and considerable water separates as an upper layerand overflows to waste (or is recycled back to the ball mill to be usedto slurry additional ore) leaving in the thickener a high viscosity buteasily pumpable slurry; from the thickener the so thickened slurry ofrecovered mineral passes from the bottom thereof to a filter systemwhich is preferably a vacuum dewatering type which comprises envelopesconnected to an internal vacuum system to provide interior low pressure,arranged on a wheel which rotates on a horizontal axis so as to definean arc passing below the upper surface of the body of the thickenedmineral slurry, causing slurry to adhere to the outside as a wet cakeand water to be removed therefrom through the internal vacuum system,and to rotate through a second are above the surface of the slurry wherethe envelopes scrape against fixed blades which remove the cake as wetcrumbles; from thence the cake crumbles drop onto a conveyor and areconveyed to dryers which produce a dehydrated commercially acceptableCaF product.

All necessary crushers, ball mills, conveyors, treating compound inletand feed lines, transfer lines, control valves and pumps, rougher cellsequipped for mechanical agitation, aerating and collection means,conditioning and thickener tanks, vacuum dehydration means, and dryers(all of which are known in the art) are located in accordance with arecommended lay-out suggested by advanced technology of ore treatmentprocessing.

The improvement, in broad terms, of the above conventional generalprocedure and equipment which is the instant invention, comprises amethod and means of continuous measurement of density differential of amineral slurry at selected successive stages in a flotation system whichdifferential is continuously recorded and serves as a basis forjudicious adjustment of at least one component or condition of theprocess and provides for prompt adjustment thereof, e. g., a componentof the feed composition in accordance with the density differential, toprovide optimum recovery and improved quality of product. This isattained inherently in the novel system by converting the densitydifferential to a pressure differential which is transferred as apneumatic impulse. This may be done by directing the impulse to arecording instrument which is observed and acted on. The impulsepreferably, however, is directed to an optimizer which automaticallydirectly adjusts an ingredient in the feed to that proportion whichresults in the highest per cent recovery which is consistent with goodquality. This is a peak-seeking optimizer which continuously changes theselected ingredient to result in optimum density differential.

The novel aspects and mode of operation of the improved process of theinvention include cooperating mechanisms (the most critical of which areidentified immediately below by small letters) for obtaining continuousdensity values converted to pressure differential employing (a)open-bottomed tubes (called hereafter density probes) positionedsubstantially vertically in the slurry at selected successive stages ofthe process, which connect at the top with tubing filled with dead airwhich terminate in (b) a two-chambered density cell, against a flexiblediaphragm therein, which forms the density cells where, by densityvariations, the densities are converted to corresponding pressurevariations in each chamber, called herein D and D respectively, for theselected stages. The differential between D, and D is either calculatedand a pneumatic impulse sent to a recording meter for quick reading andmanual adjustment made or an impulse is sent directly to (c) anoptimizer which optimizer continuously seeks the greatest D,D or peakvalue possible and automatically relays this directly to a control whichadjusts a component or condition so as to maintain the highest D,Dvalue.

If desired, the pneumatic impulse from the density pressure cell may goboth to the recording meter and to the optimizer whereby the potentialdifference in the slurry (which as aforesaid for practical purposes maybe thought of as the pH value) is made of record but wherein the changeis promptly made automatically by the peak-seeking optimizer. To attainthis latter end, an electric line or pneumatic conduit leads from theoptimizer (or continues from the meter) to an electric motor whichactuates the valves that control that component of the feed which mustbe changed to result in the desired optimum condition, viz. optimumelectric potential in the slurry being processed which in turn maintainsa large density differential which results in increased productrecovery.

It is to be understood that the invention may be practiced by employingvariations and modifications of the above procedure so long as theconcept of density measurement and automatic optimum adjustment ofdensity, in accordance with the invention, is practiced.

The optimizer is available from instrument specialists e.g., Model 571Syncro Optimizer MS-27670l, as described and illustrated in OperatingInstructions for said model published by Moore products Co., SpringHouse, Pennsylvania.

DESCRIPTION OF THE DRAWING The drawing schematically illustrates anembodiment of the apparatus of the invention and that used to practicethe method of the invention.

FIG. 1 shows the various parts of the assembled apparatus and theworking relationship of a flotation system for carrying out the processof the invention.

FIG. 2 is a schematic view of an embodiment of the density measuringinstrument of the invention wherein a fixed level is established betweenthe lower ends of two cooperative probes which constitute one instrumentto obtain a single reading. It is used where the surface level of theliquid under control fluctuates.

FIG. 3 is a schematic view of two instruments from which D and U and thedifferential thereof, of successive stages of a flotation operation,including the instrumentation referred to as (a) to (0) above, areshown.

FIG. 4 is a graph whereon the AD, i.e. D' -D' density differential asread on the recorder and guided by the optimizer, is curve (1) and asobtained manually is curve (2); and the pH values as established byautomatic adjustment according to the invention is curve (3); and the pHvalues as taken manually are curve (4).

FIGS. 5 and 6 are percent recovery values plotted against pH values ofthe slurry.

In the drawing the word conduit is used for tube connections filled withair which effectuate desired changes by pneumatic impulses. The wordline refers to flow lines for liquids. Electric connections are referredto as wires or wiring.

In more detail, the significant members of the assembled flotationsystem of FIG. 1 are represented by the following designations:

Item 2 is a moving endless apron for conveying crushed ore from a mineor storage pile. Item 3 supplies water (which need be neither deionizednor softened for use in the invention). Line 4 supplies a suppressant,e.g., an aqueous solution of quebracho. Both 3 and 4 lead into line 5which bifurcates, through control valves (a) and (b), into lines 6 and7, respectively. Tank 8 supplies an alkalinity control agent, e.g., anaqueous solution of soda ash, which connects with line 101. Lines 6 and10 supply water and conditioning agents to the ore as it enters, andline 7 as the ore leaves, ball mill 12 (i.e., a drum rotating on asubstantially horizontal axis or inclined slightly towards the outletend, and containing freely moving steel balls for grinding ore). Item 13is the outlet line from 12 which by means of pump (p) powered by motor(m) conveys slurry to 14 which is a cyclone separator of coarser andfiner grind ore (in aqueous slurry containing the additives). Item 16 isan outlet line for finer grind ore from 14 leading directly to furtherprocessing and line 18 is an outlet line for coarser grind ore from 14'leading back to 12 for regrinding. Instrument 19 positioned in line 16is a total ore volume measuring instrument which is connected byelectric wire 20 to the first of two pens on recording instrument 21which records hourly total ore volume thereon. Line 16 terminates inconditioning tank 22 known as a conditioner for finely ground ore slurryfrom the ball mill, provided with a high speed agitator (A). Positionedin 22 are electrodes T and S comprising electrode pair 24 made oferosion-resistant material (as described in co-pending application Ser.No. 219,230, entitled METHOD OF CONTINUOUS MEASUREMENT AND CONTROL OFFLOTATION CONDITIONS", of Porter Hart, filed concurrently herewith)which are provided with electric wiring 25 connected thereto and leadingto a first recording pen which records continuously the electrodepotential, which for simplicity may be considered to be the alkalinityof the slurry, on meter 26 (which for practical purposes may beconsidered a pH meter). Electrodes 24 are not essential to the practiceof the invention but give an accurate slurry EMF (which for simplicityas indicated may be called pH value) at any time-and serve as anindependent source of knowledge of the conditions of operation.

Feeding into 22 is a surface tension improver or col lector agent, e.g.,oleic acid, by means of system 27.

Also in conditioner 22 there are shown a pair of cooperating verticaltubes 28, open at the bottom and containing air as shown in FIG. 2. Theyare, as shown on FIG. 2, immersed to different depths in the slurry,e.g., a difference in depth of about twenty to thirty inches between theopen lower ends, thereby defining a fixed stratum or layer of slurry.upon which to calculate the slurry density. By means of conduits 29 andinstrument 30 (a pressure-density cell) there is provided an accuratedensity reading D by reason of corresponding pressure changes. This Dvalue is conveyed through conduit 31 into three conduits, viz: 32, 33,34: conduit 32 leads to computer 35 where the volume (V) value frommeter 21 through conduit 36 is received and the calculation V X D, massflow is made and the result sent by pneumatic signal through conduit 37to a second pen on meter 21 for recording mass flow thereon. Conduit 33leads to computer 38 to provide the D, value to the computer. Conduit 34leads to a first pen on meter 39 which records the D value continuously.Conduit 40 leads from meter 39 to valves (a) and (b): valve (a) providesautomatic control of water containing quebracho into line 6 for entranceto ball mill 12 and valve (b) provides automatic control of watercontaining quebracho into line 7 as the slurry leaves ball mill 12. k

Line 41 leads conditioned ore from 22 to cell 01, the first of theseries of rougher cells designated collectively item 42. Density probetube 44 (similar to the longer tube of 28 and described more fullyhereinbelow), is submerged in cell C-l. Via air conduit 46.. the densityD' of the slurry in cell C-l (converted to corresponding pressure)deflects a flexible diaphragm in accordance therewith, in two-chambereddensitypressure instrument 48. Cell 06, the sixth. of rougher cells 42,is provided with density probe 50 (similar to probe 44 of cell C-l)which by way of conduit 52 converts the density D' of the slurry in cellC-6 to pressure which also tends to deflect the flexible diaphragm indensity-pressure instrument 48 (against the opposing pressure responsiveto the density of O1), in accordance with the pressure changes. By meansof the pressure-activated diaphragm positioned between the two chambersin 48, a pneumatic impulse, responsive to the pressure differential, ispassed along conduit 54, sending one signal into optimizer 56 and asecond signal through conduit 58 to a second pen on meter 26 whichcontinuously registers the actual, i.e., existing, D -D, or AD value forpurposes of record.

Optimizer 56 continuously and automatically seeks the greatest densitydifferential (D',D' since the greater differential in density indicatesthe greatest efficiency of the rougher cells. An important condition forhigh recovery is the correct amount of alkalinity control agent (usuallysoda ash solution) added. Exact and quick adjustment of soda ash isaccomplished by the optimizer passing optimum desired pH value signals,via conduit 59, to a pointer on meter 26 where they are continuouslyindicated for reference purposes and which the pH recording pen thereontends to follow. However, by means of conduit 61, the optimizerguidedpneumatic impulses are promptly passed on through branching conduits 62and 63 to valves 0 and d, respectively which, by means of gap controller64, control two branch flows from soda ash supply system, of thealkalinity control additive (e.g., an aqueous solution of soda ash).Valve c regulates flow through line 10 to ball mill 12 and valve dregulates flow through line 65 to conditioner 22 in desired proportions,usually about twice as much being directed to 12 as to 22. It should beunderstood that soda ash is used here for illustrative purposes. Forsome ores it is necessary that flotation be conducted in a neutral oracid medium, i.e., at a relatively low pH and an acidifying agent wouldbe added.

An air supply system is represented by source 66, main conduit 67, andbranches 68, 69, and 70, which system provides available pneumaticpressure as needed in the various conduits for automatic control.

As the slurry is moved from cell to cell in roughers 42, leaving eachpreceding cell and entering the next succeeding cell, while beingagitated and while air is blown upwardly therethrough foam is producedwhich carries CaF to the top of the cells and froths it off into thecollecting troughs 82.

A third density probe 72 (of the type designated 44 and 50) is immersedin cell C-8 whereby density D value is obtained by means of conduit 73leading to pressure-density diaphragm cell 74. The D value of C-8 isconveyed therefrom via conduit 76 to a second pen on meter 39 whereby Dis recorded. Branching off of conduit 76 is conduit 77 which feeds the Dvalue into computer 38 for calculating D,D /D, percent recovery (percentR). This percent R value is conveyed by pneumatic signal via conduit 79to a third pen on meter 39 whereby it is recorded.

The slurry which has not been frothed off in roughers 42 passes from apoint near the bottom of cell C-8 through line 8ll and, by means of pumpp and motor assembly m, is forced to a tailings pit or pile.

The high Cal content material, i.e., concentrates, from roughers 42 isfrothed off into collecting trough system 82 from which it ultimatelypasses through line 83 to cleaners designated collectively 84, which areactually additional flotation cells (and not always necessary) and whichare very similar to 42 but which are designed to accept the once-frothedoff ore as feed which is of much higher CaF content than slurried freshore feed. That portion of the slurried concentrates which is not frothedoff at cleaners 84 (similarly as from roughers 42) passes out from apoint near the bottom of the last cleaner cell through line 85 into line81 and thence to the tailings pile. The recovered froth from cleanercells 84 passes into collecting troughs 86 and ultimately into line 87leading to thickener vessel 88 under slow agitation where a largepercent of the water content thereof rises to the top and overflows towaste (or is recycled for reuse with fresh ore) as the concentratessettle toward the bottom and thickens. From thickener 88, as a highviscosity fluid, the CaF is drawn off the bottom of 88 through line 89into filter system 90 comprising envelopes which are subjected tointerior vacuum, alternately being submerged in the thickened slurrywhich clings thereto to form a cake, and thence being brought out of theslurry into contact with fixed scraper blades that remove the cake (notshown in detail). The rotating envelopes and stationary blades areidentified schematically as items 91 and 92, respectively.

The so removed cake (now wet crumbles) is passed via conveyor 94 todryer 96, which in practice customarily consists of a series ofconnected drying units, which produces a 97.4 percent or higheranhydrous CaF powder.

Although pneumatically operated controls are shown in the illustration,it should be understood that, other than the pressure impulses receivedfrom the density probes by the pressure cells, all signals may betransferred and measured by means of an electric system.

FIG. 2 shows two tubes in combination to define a fixed depth or stratumto obtain a single density value (where the level in the containervaries) so that the volume at which density (D is measured remains thesame. It is used, for example, when the density is obtained fromconditioner 22. Since air must be provided to maintain adequate andsubstantially dead air in the probes, a metering valve, opening foradmission of air without objectionable accompanying air currents, isprovided in each of the two tubes comprising the probe.

FIG. 3 shows in some detail the assembly comprising density probes 44and 50, conduit 46 leading from probe 44 and conduit 52 leading fromprobe 50 to opposing chambers D', and D g of density-pressuredifferential instrument 48. The probes, as aforesaid, are elongatedhollow cylinders which are open at the bottom and closed at the top toform dead-end systems terminating at the flexible diaphragm whichseparates 48 into D and D chambers. The diaphragm responds to slightchanges in pressure differential thereagainst which changes are promptlytransferred from instrument 48 via conduit 54 to optimizer S6 and thencevia conduit 59 to meter 26. The pneumatic impulses recorded on meter 26are passed on via conduit 61 to gap controller 64 and valves c and d.Stirring and air supply assemblies are schematically represented and solabeled. Ample air is provided in tube probes 44 and 50 by air enteringthe cell bottoms for flotation.

FIG. 4 clearly demonstrates the improved control leading to assuredimproved efflciency and higher percent recovery attained by the practiceof the invention.

FIG. 5 shows the percent CaF recovered at increasing slurry pH values toshow that recovery is substantially zero at too low or too high slurryEMF, herein referred to as pH values.

FIG. 6 shows that the percent CaF recovered remains high as the pHvalues are clustered about the optimum value as automatically set by theoptimizer as it receives the signals from the pressure-density cell, thesignals being in prompt response to the density differential based ondensities measured by the probes in accordance with the invention.

The density probe for D need not be positioned in the cell selected inFIG. 1, although such is preferred. Any succeeding cell after cell C-lcan be used. Since by far the major portion of the flotation has beenconsumated by the time the slurry has passed from cell C-6, that cell isselected for illustration. The remaining cells, viz. cells C-7 and C-8of FIG. 1, often called scavenger cells, froth ofl very littleadditional CaF and sometimes none. However the D probe could besatisfactorily placed in cell 08 rather than cell C6 to provide forautomatic adjustment of the additament required to maintain optimumconditions. C-1 and G6 are selected for D, and D density values becausea preponderance of the flotation is attained therebetween within arelatively short time and therefore automatic adjustments based thereonare made as promptly as possible.

The principal use of D density, i.e., the density of the unfrothedslurry, is for the purpose of controlling the total solids, (i.e.,amount of water added to the ore) in the ball mill. D is the density ofthe tailings. Both values are used for the calculation: D -D /D to givethe overall percent CaF recovery.

EXAMPLES To illustrate the practice of the invention in comparison withconventional practice employing as nearly as possible the same milllay-out, ore, and processing techniques except that, in the practice ofthe invention, the hereinafter claimed density-pressure probes andoptimizer control of soda ash were employed whereas control wasexercised in the conventional or comparative example in accordance withthe most efficient techniques known prior to the instant invention.

The most significant operating conditions and results obtained forillustrative and comparative examples are shown in Table I.

Comparative This example was conducted to illustrate the recovery of CaFfrom fluorspar ore in accordance with conventional practice. Completedaily records were maintained for a prolonged period of continuousoperation. The procedure followed consisted of feeding crushed fluorsparore by way of conveyor 2 into ball mill 12 as shown in FIG. 1 into whichwere also fed 10 percent by weight aqueous solutions of quebracho andsoda ash and sufficient water to provide the desired solids. The

ples are shown in Table I.

ore was thereby converted to a conditioned slurry of fine particle ore.From 12 the slurry was passed into a cyclone separator of the typedesignated 14 in FIG. 1. Therein particles coarser than 200 mesh sizewere returned to the ball mill and the finer particles were pumped to ahighly agitated conditioning tank (e.g., conditioner 22) into whichconcurrently were fed oleic acid and additional aqueous soda ashsolution controlled as needed.

From the conditioner the substantially uniformly mixed treated oreslurry was caused to flow to the se ries of flotation (rougher) cells asrepresented by 42 of the drawing.

Air was released into each cell near the bottom center by way of anannular opening about the shaft of a rotating stirrer-centrifugal pumpassembly (illustrated in FIG. 3) vertically positioned in each cell toproduce froth. The CaF being attracted to the froth in the cells, roseto the top thereof, was caused to overflow, and was collected as aslurry in troughs positioned along the outer edges, where, aided bylimited additional water flow, it was drained away, and thereaftersubjected to a second flotation treatment in similar series of cellsknown as cleaners, e.g., 84 of FIG. 1 of the drawing. The uncollectedportion of the slurry in rougher cells 42 was drained away to a tailingspond as also was the uncollected portion of cleaner cells 84. Therecovered froth from the cleaners 84, usually aided by more additionalwater for satisfactory flow, was pumped to a relatively large moderatelyheated tank 88, called a thickener, provided with very slow agitationwherein an appreciable amount of the water present continued to rise andwas separated by its overflowing. From 88 the thickened paste-likeslurry was flowed at a controlled rate from the bottom thereof to filter(dewatering) system 90 comprising exhausted envelopes, i.e., envelopes91 having a vacuum applied to the interior causing the thickened slurryto cling to the exterior, whereby moisture was drawn inwardly from theslurry by the vacuum leaving a cake-like layer on the envelopeexteriors. This layer was removed by causing the envelopes to rotateagainst fixed scraper knives or blades 92 (or if more convenient theknives may be moved across the envelopes) causing the wet recoveredmineral to fall in crumbles on a conveyor, e.g., 94, and be taken intothe first of a series of dryers represented by 96. The dryer produced ananhydrous CaF product.

The only process control practiced in the above'conventional operation,other than observation and hand feel consisted essentially of oreanalyses, periodic sampling for manual determinations of both .pH anddensity, and laboratory analyses of the periodic sami The conditions andresults of the conventional exam- Example of the Invention The followingexample is illustrative of the practice 7 of the invention. Asaforesaid,'the rate of feed of ore,

the additives, and flotation principles applied and the general flowpattern were substantially the same as in the above comparative exampleexcept that the techniques applied tothe control of the process werethose of the invention.

By the term positive-negative electrical potential as used herein ismeant any variation in electrode potential in a 7 In accordance with theinvention the pair of density probe tubes 28 in conditioner 22 werepositioned so that the vertical distance between their lower open endswas 25 inches, thus giving a fixed stratum or layer of slurry formeasurement of density. Likewise, by inserting single density probetubes 44 and 50, respectively, in rougher cells C-1 and 06, so thattheir open ends were 15 inches above the bottom of the cells, a fixedstratum of slurry was defined since the cellsware maintained full ofliquid at all times during the flotation operation. The top of tubes 44and 50 led into smaller flexible tubing lines 46 and 52, respectively,which dead-ended on opposite sides of the diaphragm in D,D meter 48which converted the density values of the contents of cells C-1 and G6to a pressure differential which was transmitted via conduit 54 tooptimizer 56 which translated the pressure differential to the desiredEMF potential (which may be considered pH value) corresponding tomaximum pressure differential. Conduit 59 carried the pneumatic impulseto 26 where it was indicated as the optimizer-guided desired pH value.Conduit 61 further relayed the pneumatic impulses from optimizer 56 viaconduit 62 and 63 to motor valves c and d .whereby adjustments wereautomatically made in soda ash feed, by means of gap controller 64,which tended continuously to maintain an optimum feed composition. Thecells 42, cleaners 80, thickener 88, filter assembly 90, and dryers 96,were employed as in the conventional examples.

By means of the peak-seeking optimizer 56, that pH was maintained whichcaused the A density, and hence percent CaF recovered, to remain at thetop of the curve shown in FIG. 6. The optimizer attains this objectiveby continuously adjusting the rate of aqueous soda ash solution flowtoward maximum density, i.e., whenever increments in soda ash continueto increasetheA density, such increments continue to' be made but whensuch increments result in a decrease in A density, the optimizerimmediately calls for a reduction in soda ash and continues to make suchreductions until the A density again is not improved by such decreases.

TABLE I Kgm/ min. aq. 10%

of sol. aq. CaF,

CaF of soda CaF Product Ore availqueash Oleic probased CaF Feed CaF,able bracho soln. acid duct on CaF, in [(gm/ in in mi] ml/ ml/Conditioner Kgm/ ore CaF, Min. Ore Ore min min. min. T.S. Ternp.C. min.Content Product Comparative (conventional) Examples 140.28 58.0 81.4500-900 12004300 3-5 32-33 110-130 5000 61.5 97.4 130.50 67.3 87.75001000 1100-4500 3-5 32-33 1 10130 55.50 63.3 97.4

Examplg 1 of the Invention ra Total solids Reference to Table I clearlyshows a number of significant advantages due to the practice of theinvention. Although exactly the same mill was employed for all examples,except for the use of the instrumentation of the invention, thefollowing benefits of the invention are clearly realized:

I. the amount of ore, i.e., the rate of feed, that can be put throughthe mill is far greater;

2. the amount of quebracho (suppressant) required was steady;

3. the amount of soda ash was controlled within narrower limits;

4. the amount of oleic acid (collector agent) required was less;

5. the temperature in the conditioner was held more steady;

6. the percent of CaF product (of the same purity) recovered, based uponthe CaF available in the ore, was considerably higher. (It is estimatedthat 1 percent greater recovery has a money value of about $500 per 100tons of ore processed).

Although not specifically shown on the table, operation according to theinvention was much more steady: the pH reading fluctuated over a muchnarrower range; the rate of ore feed and the periodic analyses of therecovered product showed less variation. The elimination of the manhours required for sampling the slurry and taking the pH and density byconventional methods released operators for other duties.

The percent of SiO and CaCO in the CaF- product were less than in thatproduced conventionally.

EXAMPLE 2 Shortly after the optimizer-density probe assembly of theinvention had been installed, calibrated, and conditions stabilized, itwas employed to guide and control a production size operation for 24hours. The analysis of the ore being processed showed 76.80 percent CaF12.0 percent CaCO 7.68 percent Si0 and about 1,000 ppm Be.Simultaneously with the practice of the invention, the slurry in processwas sampled, the pH value and D and D density values obtained accordingto conventional procedures, and indicated changes that normally wouldhave been made (but in fact were not) recorded every hour. The pHvalues, D' D' and hence D, less D were automatically regulated inaccordance with the invention. (Note that D is taken in conditioner 22and D in cell C-8; D is taken in cell C-1 and D in cell 08).

The optimizer through its peak-seeking principle continued to change therate of addition of the soda ash solution at pre-selected intervals ofsiz minutes, increasing the rate of flow thereof so long as the densitydifferential increased, but when such increase in flow of soda ashceased to increase the density differential, reversing direction anddecreasing the rate of flow of soda ash so long as the densitydifferential was not decreased by such decreased flow.

The percent CaF recovery, based on the CaF content of the ore, isdirectly related to the D less D value and is calculated by D,D /D

The production unit was started at 8 a.m. and continued until 8 am. ofthe following morning, following the method of the invention. Manualtests were taken regularly and calculations made based thereon but suchtests were not used to control the operation.

TABLE 11 Percent Cal- Product Recovered Based on Cal- Content of OreActual p fi \m calculated Recovery From Recovery if Based on OptimizerOperation Optimizer Density Had been Density Manually Probe Guided byProbe Time Taken Control Manual Tests Control 8 9.7 9.35 52.2 59.6 9 9.49.35 64.2 72.6 I 10 9.5 9.35 60.8 68.5 11 9.3 9.30 64.2 70.3 12 9.2 9.3074.0 71.6 RM.

Reference to Table II evinces convincingly the more reliable controlpromptly and effectively made by the practice of the invention.

Below is a summary showing the real recovery ac- 1 cording to theinvention and the recovery that would have been made had conventionalpractices been followed, i.e., had the manual sampling and the pH anddensity values which were thereby obtained been used to adjust the rateof flow of ore, water, and soda ash solution. The summary shows thesuperior performance of the method of the invention employing therequired apparatus of the invention.

I Average Per Cent Recovery Manual Optimizer-Density Shifts OperationCell Control 8 am. to 4 pm. 65.0% 68.6% D P)M) TO AB P)M) 61.3% 66.5% 12pm. to 8 am. 63.5% 69.8%

Having described my invention, what I claim and desire to protect byLetters Patent is:

1. In the recovery of mineral values from an ore slurry employingflotation principles wherein conditioning agents are admixed with waterand pulverulent ore to make a treated slurry and said slurry issubjected to flotation by passing air upwardly through the agitatedslurry in successive connected cells whereby the mineral sought to berecovered is collected in a froth which is overflowed and recovered fromthe thus provided overflow, the improvement comprising:

continuously measuring the density values of at least two of said cells,continuously converting the density values to a pressure differentialwhich is proportional to the differential of density values;

causing a pneumatic impulse in accordance with variations in thepressure differential to be relayed to a continuous registeringinstrument to provide a continuous pressure differential record which iscalibrated to show density differential;

adjusting at least one additive of the flotation process in accordancewith the recorded density differential to tend to maintain saiddifferential at a maximum.

2. The method according to claim 1 wherein the electrical potential(EMF) value of the slurry prior to its tential can be adjusted inaccordance with changes in said density differential.

3. The method according to claim 2 wherein the electrical potential(EMF) is calibrated into pH values.

4. The method according to claim 1 wherein a pneumatic impulse inaccordance with said pressure differential, as controlled and determinedby said density differential, is continuously sent to an optimizer whichautomatically seeks the maximum density differential which iscontinuously recorded.

5. The method according to claim 4 wherein said maximum densitydifferential is continuously converted to pH values and such values usedto guide the amount of an ingredient which, when admixed with theslurry, modifies the electrical potential (EMF) thereof.

6. The method according to claim 4 wherein a series of pneumaticimpulses provided by said optimizer are sent to the feed control of aningredient which modifies the electrical potential (EMF) in the slurryand increases or decreases the rate of said feed to cause the potentialto trend at predetermined time intervals in the direction of maximumdensity differential in the slurry bath in the two cells being measured.

7. The method according to claim 6 wherein the optimum positive-negativepotential differential in the slurry bath is recorded as well asautomaticadjustment made of the rate of feed of a positive-negativemodifying ingredient to continue to modify that rate to one which givesmaximum density differential between the density of the slurry at ornear the beginning and that at or near the end of the flotationoperation.

8. An apparatus for continuously measuring, recording and controlling anore flotation process which comprises in combination:

1. at least two independently operating vertically positioned elongatedhollow probes, open at the lower end, each immersed to substantially thesame depth in a body of ore slurry, each probe being located at one ofselected successive flotation stages and filled with a non-turbulentgas, substantially chemically unreactive with the slurry;

2. a tube extending from the upper end of each of said probes leading toopposite sides of a closed bichambered pressure-sensitive instrument,the chambers being formed by a dividing flexible membrane, therebyproviding entrapped substantially dead gas in each probe-tube chambercombination, the pressure of which increases or decreases directly inresponse to the density of the liquid at the level of the lower end ofeach of said probes and deflects said membrane in accordance with thepressure differential and therefore in accordance with the densitydifferential;

3. means for continuously measuring the electrical potential (EMF) ofthe ore slurry at a location prior to the first flotation stage andmeans for recording and adjusting said electrical potential; and

4. a peak-seeking optimizer responsive to the pressure differentialprovided by said pressure-sensitive instrument and which adjusts thesaid electrical potential (EMF) of the slurry at said location prior tothe first flotation stage at the optimum necessary to maintain thepressure differential (and thus the ore recovery) at a maximum.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO.3,834,529 Q DATED September 10, 1974 INVENTOR(S) I Porter Hart it iscertified that error appears in the ab0ve-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 13, line 19, "DP)M) TO ABP)M)" should be changed to 4 p.m. to 12p.m.

O Signed andfiealed this second Day Of September 1975 [SEAL] Arrest.

RUTH c. MASON c. MARSHALL DANN ilrzsn'ng Officer (ummissr'mrcruj'lulcntx and Trademarks

1. In the recovery of mineral values from an ore slurry employingflotation principles wherein conditioning agents are admixed with waterand pulverulent ore to make a treated slurry and said slurry issubjected to flotation by passing air upwardly through the agitatedslurry in successive connected cells whereby the mineral sOught to berecovered is collected in a froth which is overflowed and recovered fromthe thus provided overflow, the improvement comprising: continuouslymeasuring the density values of at least two of said cells, continuouslyconverting the density values to a pressure differential which isproportional to the differential of density values; causing a pneumaticimpulse in accordance with variations in the pressure differential to berelayed to a continuous registering instrument to provide a continuouspressure differential record which is calibrated to show densitydifferential; adjusting at least one additive of the flotation processin accordance with the recorded density differential to tend to maintainsaid differential at a maximum.
 2. The method according to claim 1wherein the electrical potential (EMF) value of the slurry prior to itsbeing subjected to flotation is continuously recorded so that, forpurposes of process control, said electrical potential can be adjustedin accordance with changes in said density differential.
 2. a tubeextending from the upper end of each of said probes leading to oppositesides of a closed bi-chambered pressure-sensitive instrument, thechambers being formed by a dividing flexible membrane, thereby providingentrapped substantially dead gas in each probe-tube chamber combination,the pressure of which increases or decreases directly in response to thedensity of the liquid at the level of the lower end of each of saidprobes and deflects said membrane in accordance with the pressuredifferential and therefore in accordance with the density differential;3. means for continuously measuring the electrical potential (EMF) ofthe ore slurry at a location prior to the first flotation stage andmeans for recording and adjusting said electrical potential; and
 3. Themethod according to claim 2 wherein the electrical potential (EMF) iscalibrated into pH values.
 4. a peak-seeking optimizer responsive to thepressure differential provided by said pressure-sensitive instrument andwhich adjusts the said eleCtrical potential (EMF) of the slurry at saidlocation prior to the first flotation stage at the optimum necessary tomaintain the pressure differential (and thus the ore recovery) at amaximum.
 4. The method according to claim 1 wherein a pneumatic impulsein accordance with said pressure differential, as controlled anddetermined by said density differential, is continuously sent to anoptimizer which automatically seeks the maximum density differentialwhich is continuously recorded.
 5. The method according to claim 4wherein said maximum density differential is continuously converted topH values and such values used to guide the amount of an ingredientwhich, when admixed with the slurry, modifies the electrical potential(EMF) thereof.
 6. The method according to claim 4 wherein a series ofpneumatic impulses provided by said optimizer are sent to the feedcontrol of an ingredient which modifies the electrical potential (EMF)in the slurry and increases or decreases the rate of said feed to causethe potential to trend at predetermined time intervals in the directionof maximum density differential in the slurry bath in the two cellsbeing measured.
 7. The method according to claim 6 wherein the optimumpositive-negative potential differential in the slurry bath is recordedas well as automatic adjustment made of the rate of feed of apositive-negative modifying ingredient to continue to modify that rateto one which gives maximum density differential between the density ofthe slurry at or near the beginning and that at or near the end of theflotation operation.
 8. An apparatus for continuously measuring,recording and controlling an ore flotation process which comprises incombination: